Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
2002-03-01
2003-01-07
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C427S455000
Reexamination Certificate
active
06503290
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a chromium-tungsten or tungsten-chromium alloy powder for forming coatings or objects having an excellent combination of corrosion and wear properties.
BACKGROUND ART
Hard surface coating metals and alloys have long been known. For example, chromium metal has been used as an electroplated coating for many years to restore worn or damaged parts to their original dimensions, to increase wear and corrosion resistance, and to reduce friction. Hard chromium electroplate, however, has a number of limitations. When the configuration of the part becomes complex, obtaining a uniform coating thickness by electro-deposition is difficult. A non-uniform coating thickness necessitates grinding to a finished surface configuration, which is both difficult and expensive with electroplated chromium. These disadvantages arise from chromium's inherent brittleness and hardness. Furthermore, chromium electroplating has a relatively low deposition rate and often requires a substantial capital investment in plating equipment. In addition to this, it is often necessary to apply one or more undercoats, or to use expensive surface cleaning and etching procedures to prepare substrates for chromium deposition. Disposal of spent plating baths also adds significantly to the cost of the process.
An alternative method of depositing chromium metal is by metal spraying such as with a plasma or detonation gun. This method allows the coating to be applied to almost any metallic substrate without using undercoats. The rate of deposition is very high, minimizing the capital investment. Furthermore, the coating thickness can be controlled very closely so that any subsequent finishing can be kept to a minimum. And finally, the overspray can be easily contained and recovered making pollution control a simple matter.
Unfortunately, plasma-deposited chromium is not as wear-resistant at ambient temperature as hard electroplated chromium. This is because the wear-resistant of chromium plate is not an inherent property of elemental chromium but is believed to arise largely from impurities and stresses incorporated in the coating during plating. Plasma deposited chromium is a purer form of chromium that lacks the wear-resistant of hard chromium plate; but it retains the corrosion-resistance characteristics of electroplated hard chromium.
Improved coatings can be made by incorporating a dispersion of chromium carbide particles in a chromium matrix for wear resistance. Coatings of this type can be made from mechanical mixtures of powders. However, there are certain limitations to the quality of coatings made from them. Both plasma and detonation-gun deposition result in a coating with a multilayer structure of overlapping, thin, lamella or “splats.” Each splat is derived from a single particle of the powder used to produce the coating. There is little, if any, combining or alloying of two or more powder particles during the coating deposition process. This results in some of the splats being completely chromium alloy and some being completely chromium carbide, with the interparticle spacing being controlled by the sizes of the initial chromium and chromium carbide powder particles. J. F. Pelton, in U.S. Pat. No. 3,846,084 describes a powder in which substantially every particle consists of a mixture of chromium and chromium carbides. The powder of this patent produces a coating wherein each splat is a mixture of chromium and chromium carbides.
Hard surface coatings can also be made using sintered cobalt structures that encapsulate tungsten carbide particles. These alloys however have undesirably high porosity for some applications and are limited in their tungsten carbide content.
Alloys containing carbides of tungsten, chromium, and nickel have been used in hard surfacing. For example, Kruske et al., in U.S. Pat. No. 4,231,793, disclose an alloy containing from 2 to 15 weight percent tungsten, 25 to 55 weight percent chromium, 0.5 to 5 weight percent carbon, and amounts of iron, boron, silicon, and phosphorus that do not exceed 5 weight percent each, with the balance being nickel. Similarly, S.C. DuBois, in U.S. Pat. No. 4,731,253 disclose an alloy containing from 3 to 14 weight percent tungsten, 22 to 36 weight percent chromium, 0.5 to 1.7 weight percent carbon, 0.5 to 2 weight percent boron, 1.0 to 2.8 weight percent and a balance of nickel.
S. C. DuBois describes another hard surfacing alloy containing tungsten and chromium in U.S. Pat. No. 5,141,571. The tungsten content of this alloy is from 12 to 20 weight percent, the chromium content is from 13 to 30 weight percent, and the carbon content is from 0.5 to 1 weight percent. The alloy also contains from 2 to 5 percent each of iron, boron, and silicon, with the balance being nickel. This hard facing alloy contains embedded tungsten carbide and chromium carbide crystals.
Cabot Corporation (Now Haynes Intl.) published a group of corrosion resistant alloys referred to as the “Stellite Alloys” in its 1982 brochure entitled
“Stellite Surfacing Alloy Powders”
(Stellite is a registered trademark of Deloro Stellite Inc.). The Stellite alloy compositions disclosed in this reference contain from 0 to 15 percent tungsten, from 19 to 30 weight percent chromium, from 0.1 to 2.5 weight percent carbon, up to 22 weight percent nickel, and amounts of iron, boron and silicon that do not exceed 3 weight percent each, with the balance being cobalt.
SUMMARY OF THE INVENTION
The invention is a corrosion resistant powder useful for deposition through thermal spray devices. The powder consists essentially of, by weight percent, about 30 to 60 tungsten, about 27 to 60 chromium, about 1.5 to 6 carbon, a total of about 10 to 40 cobalt plus nickel and incidental impurities plus melting point suppressants. This corrosion resistant powder is useful for forming coatings having the same composition.
REFERENCES:
patent: 2124020 (1938-07-01), Wirth
patent: 3846084 (1974-11-01), Pelton
patent: 4123266 (1978-10-01), Foley et al.
patent: 4224382 (1980-09-01), Brown et al.
patent: 4231793 (1980-11-01), Kruske et al.
patent: 4353742 (1982-10-01), Crook
patent: 4519840 (1985-05-01), Jackson et al.
patent: 4626476 (1986-12-01), Londry et al.
patent: 4731253 (1988-03-01), DuBois
patent: 4999255 (1991-03-01), Jackson et al.
patent: 5030519 (1991-07-01), Scruggs et al.
patent: 5102452 (1992-04-01), Taskinen et al.
patent: 5141571 (1992-08-01), DuBois
patent: 5387294 (1995-02-01), DuBois
patent: 5419976 (1995-05-01), Dulin
patent: 5514328 (1996-05-01), Menon et al.
patent: 5611306 (1997-03-01), Takano
patent: 5863618 (1999-01-01), Jarosinski et al.
patent: 6004372 (1999-12-01), Quets
Cabot Corporation brochure entitled “Stellite Surfacing Alloy Powders” (1982).
Jarosinski William John Crim
Temples Lewis Benton
Mai Ngoclan
O'Brien Cornelius F.
Praxair S.T. Technology, Inc.
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